Overcoming Endosomal Barrier by Amphotericin B-Loaded Dual pH-Responsive PDMA-<italic>b</italic>-PDPA Micelleplexes for siRNA Delivery

S mall interfering RNA (siRNA)-mediated RNA interference (RNAi) has received considerable attention since the discovery of the RNAi mechanism in 1998. RNAi holds great promise in molecular therapy of intractable and genetic-related human diseases by silencing the target mRNA (mRNA). 5 For systemic siRNA delivery, naked siRNA is vulnerable to serum and endogenous nuclease degradations. Furthermore, siRNA does not easily cross cellular membranes because of its large size and negatively charged potential. Nonviral carriers have been extensively investigated to improve the siRNA stability, bioavailability, and delivery efficiency to the target tissues or cells. 8 Endosomal escape is one of the major barriers for nonviral siRNA delivery, since siRNA trapped in endosomes is typically trafficked into lysosomes where siRNA is degraded. To overcome the endosomal barrier, a variety of stimuli-responsive nonviral vectors havebeenexploited. Among these, pH-responsive vectors utilizing the acidic intracellular environment via proton buffer effect (e.g., poly(ethyleneimine) (PEI), poly(L-histidine), and poly(β-amino esters)) 17 or reversible PEG shielding were extensively investigated. 20 Furthermore, amphiphilic peptides (AMP) or virusderived proteins were covalently conjugated with the polycationic vectors to enhance siRNA endosomal release by forming transmembrane pores or fusing with endosome membranes. Despite these remarkable advances, timely and efficient siRNA endosomal escape remains a considerable challenge. Recently, we reported a new set of pHactivatable micellar (pHAM) nanoparticles with tunable pH-responsive properties. These nanoparticles were produced from a series of diblock copolymers with an ionizable block with controlled hydrophobicity. One such polymer, poly(ethylene glycol)block-poly(2-(diisopropylamino) ethylmethacrylate) (PEG-b-PDPA), had a pH transition at 6.3. The PEG-b-PDPA micelles were specifically activated/dissociated in early * Address correspondence to [email protected].